Rename property 'z-stepSize' to 'zStepSize' for naming consistency and client compatibility

[ehennestad]

Summary

In gridImageStack.schema.tpl.json, the property is currently named z-stepSize:

openMINDS_core/schemas/data/gridImageStack.schema.tpl.json

Line 60 in d62e092

"z-stepSize": {

I suggest renaming this to zStepSize.

Motivation

• Hyphens in property names are not permitted in MATLAB class property identifiers.
• In openMINDS MATLAB, this forces special remapping logic for this field when generating/maintaining classes.
• z-stepSize appears non-conventional relative to other openMINDS property naming patterns and is harder for client code generation.

Proposed change

• Rename z-stepSize -> zStepSize in the schema/template.
• If needed, include a compatibility/deprecation note for downstream consumers that may still emit/read the old key.

Impact

This improves consistency and reduces avoidable client-side mapping complexity, especially for strongly typed language bindings such as openMINDS MATLAB.